Hilbert's thirteenth problem

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Hilbert's thirteenth problem is one of the 23

Using the methods pioneered by Ehrenfried Walther von Tschirnhaus (1683), Erland Samuel Bring (1786), and George Jerrard (1834), William Rowan Hamilton showed in 1836 that every seventh-degree equation can be reduced via radicals to the form ${\displaystyle x^{7}+ax^{3}+bx^{2}+cx+1=0}$.

Regarding this equation, Hilbert asked whether its solution, x, considered as a function of the three variables a, b and c, can be expressed as the composition of a finite number of two-variable functions.

Hilbert originally posed his problem for algebraic functions (Hilbert 1927, "...Existenz von algebraischen Funktionen...", i.e., "...existence of algebraic functions..."; also see Abhyankar 1997, Vitushkin 2004). However, Hilbert also asked in a later version of this problem whether there is a solution in the class of continuous functions.

A generalization of the second ("continuous") variant of the problem is the following question: can every continuous function of three variables be expressed as a composition of finitely many continuous functions of two variables? The affirmative answer to this general question was given in 1957 by Vladimir Arnold, then only nineteen years old and a student of Andrey Kolmogorov. Kolmogorov had shown in the previous year that any function of several variables can be constructed with a finite number of three-variable functions. Arnold then expanded on this work to show that only two-variable functions were in fact required, thus answering Hilbert's question when posed for the class of continuous functions.

Arnold later returned to the algebraic version of the problem, jointly with Goro Shimura (Arnold and Shimura 1976).

• MR1601178
• V. I. Arnold and Goro Shimura, Superposition of algebraic functions (1976), in Mathematical Developments Arising From Hilbert Problems, Volume 1, Proceedings of Symposia in Pure Mathematics 28 (1976), pp. 45-46.
• MR 1512361
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• MR 0213785
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• MR 2068840
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• S2CID 14000951
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• Septic equation
• Thomae's formula

• Ornes, Stephen (14 January 2021). "Mathematicians Resurrect Hilbert's 13th Problem". Quanta Magazine.